Recruited by the Demons after winning the North Brunswick Amateurs best-and-fairest, Cardwell played in the Demons seconds premiership of 1939 and remained with the club through 1940.

Enlisting in the army in late 1941 he served in Darwin and New Guinea. At one point while he was on leave from army duty, Cardwell was given the option of playing in the seniors at the same time that he was meant to be taking a long overdue honeymoon with his wife Mavis. He chose the honeymoon and lost his chance to be a VFL footballer.

After serving in the 2/1 Australian Mechanical Equipment Company he was discharged and returned to the club as a seconds selector and committee member. In 1949 was Honorary Secretary while still playing some matches.

In 1951 he was promoted to the first team secretary role, and in time became known as "The Prince of Secretaries". One of his first acts was to ban the wearing of number 13 between 1953 and 1974 as he believed it was unlucky. His success came despite having a breakdown in 1956 from the pressure of running his own business and doing the secretary job - it led Melbourne to employing him as full-time secretary.

His partnership with Norm Smith became legendary, and though they would often clash, the two were key players in delivering one of the league's most potent glory eras. In 1958 he became the first full-time secretary of a VFL club.

At the end of 1973 Cardwell announced he would resign after the 1975 season, and he made good with his promise. Ivan Moore was his replacement. He briefly returned as a consultant in 1981.